Process of producing ferrous metal articles



J y F; e BUFFUM a 2,380,385

PROCESS OF PRODUCING FERROUS METAL ARTICLES Filed 'Jan 25 1941 Patented July 31, 1945 PROCESS OF PRODUCING FERROUS METAL ARTICLES Frank G. Buifum, Chicago, Ill., assignor, by mesne assignments, to iii-Metallic Products Corporation, Chicago, 111., a corporation of Illinois Application January 25, 1941, Serial No. 375,989

9 Claims.

This invention is a ierrous metal article having a controlled heterogeneity of composition, and the method of producing it.

The accompanying drawing shows diagrammatically in Figure 1 a side elevation 01 an axe embodying one form of the invention,a suincient area being shown in longitudinal section to illustrate the invention so far as it can be illus trated; and show diagrammaticall in Figure 2 the heat treating step.

To render the detailed description. to follow easier to understand, it may be said by way of introduction that an article such as an axe is first made as a casting of conventional malleable iron, and then selected parts such as the cutting edge of an axe are transformed into what is essentially a high carbon tool steel. There is thus produced an article with the softness, toughness and resistance to crystallization characteristic of malleable iron, but selected parts oi which have the desirable characteristics of high carbon steel.-

In practicing the invention, the first step is making the usual white i'ron casting of the composition of conventional black heart malleable iron. As is well known, the composition may vary somewhat with the size or the casting and the time it will take to cool in the mold. It will generally contain from 2 to 2 /z% of carbon, which. in the original unannealed casting, will all be combined carbon. I

The casting may next be annealed in the conventional way so that all the carbon is precipitated within the body or the casting in minute irregular parti les sometimes called rosettes, thus providing a typical black heart malleable casting.

However, as the tree carbon particles may impair the appearance oi a finely finished surface without materially aflecting utility, it is sometimes desirable to anneal the casting in a pack ing containing an oxidizing agent, such as mill scale, in sumcient quantity to decarbonize only a very thin superficial film, but to reduce the carbon in the region, where free carbon might be objectionable, to from 1 to 1.3%.

The amount and concentration of the oxidizing agent would vary somewhat with the composition of the casting and the time spent in annealing. but the requisite factors for controlled operation can quite readily be determined for any given casting by very iew analyses of the annealed castings.

The next step in the process is to cold work the annealed casting, preferably by hammering so as to compact the granular structure. For some purposes, this step, may be omitted, but it will improve the quality of the finished article.

The next step isv to reheat, at least to the critical temperature, the part of the article to be modified, and, to hold it at the critical temperature until the precipitated carbon becomes combined to the amount of 1 to 1.3%, as may be desired. The remainder of the article should not be allowed to rise in temperature sufllciently to alter its composition.

To accomplish these results, the part to be modified should be heated very quickly under conditions which will provide extremely rapid heat transfer, so that the part to be modified reaches the desired temperature so quickly that not much heat is conducted to the body of the article. It is also desirable to insulate the body of the article from extraneous heat, so as to keep its temperature as low as possible.

It has been round that the most satisfactory method of providing this localized reheating is toimmerse that part of the article to be modified in a bath of molten salt, as shown in Figure 2. To prevent the body 01 thearticle from being heated either by convection currents from the surface of the bath or by radiation therefrom, there is floated upon the bath a layer perhaps inch thick of finely divided carbon.

The composition of the bath is not particularly important, except that it is generally undesirable to employ an oxidizing bath. Excellent results have been obtained by using a commercial fused salt bath containing some cyanide and commonly sold under the name "Perlton. This particular material is designed for case hardening, but, in the brief time employed in the present process, the addition of carbon to the casting is insignificant. This particular bath is commonly available, and, of course, has no tendency to produce either an oxid scale or any oxid discoloration.

It is obviously impossible to give precise directions as to time and temperature for carrying out this reheating step of the process. The recombination of free carbon proceeds more rapidly at higher temperatures than at lower ones. Therefore, if temperature is varied, the time limit of treatment must also vary.

The temperatures selected must be determined for the various types of castings which may be treated and the portions thereof to be modified. It the. temperature is too high, the re-dissolving oi the carbon may be so rapid that it cannot be stopped with any accuracy at the right point, which is when there is from 1 to 1.3% combined wherein the free carbon is reduced to the amount desired as combined carbon in the selected part, reheating the selected part at least to the critical temperature, holding it at the selected temperature for a time adjusted to cause the recombination of such part of the free carbon as to give the desired carbon content, and quenching.

6. The process of ,impartinghigh carbon steel characteristics to a selected surface portion of a blackheart malleable iron casting, consisting in heating the selected portion at least to the critical temperature by immersing it in a fused salt bath, holding this portion at the selected temperature fora time adjusted to cause the re-combination of suchv part of the free carb0n-as to give the desired carbon content while the remainder of the casting is insulated by a layer of granular material floating on the bath, and quenching. I

7. The process of making a malleable casting, a

selected surface of which has the characteristics of high carbon steel, consisting in making the conventional white iron casting, annealing in a cal temperature by immersing it in a fused salt bath, holding it at the selected temperature for a time adjusted to cause the re-combination of such part of the free carbon to give the desired carbon content while the remainder of the article is insulatedby a layer of granular insulating material floating on the bath, and quenching.

8. The process of imparting high carbon steel characteristics to a selected portion of a blackheart malleable iron casting, consisting in heating the selected portion at least to the critical temperature by immersing itin a molten bath, hold- .ing this portion at the selected temperatur for a time adjusted to cause the re-combination of such part of the free carbon as to give the desired carbon content while the remainder of the casting is insulated by a layer of material floating on the bath, and quenching.

9. The process of imparting carbon steel char acteristics to a selected portion of a blackheart malleable iron casting, consisting in heating the selected portion at least to the critical temperature by immersing it in a molten bath, holding this portion at the selected temperature for a time adjusted to cause the re-combination of such part of the free carbon as to give the desired carbon content while the remainder of the casting is insulated by a layer of carbon floating on the bath, and quenching.

FRANK G. BUFF'UM. 

